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Computer hardware michael karbo

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KarbosGuide.com. Module 1a. About data. KarbosGuide.com. Module 1a. q Next page q Previous About data page Our PCs are data processors. The PCs function is simple: to process data, and the processing is done electronically inside the CPU and between the other components. That sounds simple, but what is data, and how is it processed electronically in a PC? That is the subject of these pages. Analog data The signals, which we send each other to communicate, is data. Our daily data have many forms: sound, letters, numbers, and other characters (handwritten or printed), photos, graphics, film. All this data is in its nature analog, which means that it varies in type. In this form, the data-signals are unusable in a PC. The PC can only process concise, simple data formats. Such data can be processed very effectively. Digital data The PC is an electric unit. Therefore, it can only deal with data, which are associated with electricity. That is accomplished using electric switches, which are either off or on. You can compare with regular household switches. If the switch is off, the PC reads numeral 0. If it is on, it is read as numeral one. See the illustration below:http://www.karbosguide.com/hardware/module1a1.htm (1 of 5)7/27/2004 4:05:11 AM

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KarbosGuide.com. Module 1a. About data. With our electric switches, we can write 0 or 1. We can now start our data processing! The PC is filled with these switches (in the form of transistors). There are literally millions of those in the electronic components. Each represents either a 0 or a 1, so we can process data with millions of 0s and 1s. Please click the banners to support our work! Bits [top] Each 0 or 1 is called a bit. Bit is an abbreviation of the expression BInary digiT. It is called binary, since it is derived from the binary number system: 0 1 bithttp://www.karbosguide.com/hardware/module1a1.htm (2 of 5)7/27/2004 4:05:11 AM

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KarbosGuide.com. Module 1a. About data. 1 1 bit 0110 4 bit 01101011 8 bit The binary number system [top] The binary number system is made up of digits, just like our common decimal system (10 digit system). But, while the decimal system uses digits 0 through 9, the binary system only uses digits 0 and 1. If you are interested in understanding the binary number system, then here is a brief course. See if you can follow the system. See how numbers are constructed in the binary system, using only 0s and 1s: Numbers, as known in the Same numbers in binary decimal-system system 0 0 1 1 2 10 3 11 4 100 5 101 6 110 7 111 8 1000 Digital data [top]http://www.karbosguide.com/hardware/module1a1.htm (3 of 5)7/27/2004 4:05:11 AM

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KarbosGuide.com. Module 1a. About data. We have seen that the PC appears capable of handling data, if it can receive them as 0s and 1s. This data format is called digital. If we can translate our daily data from their analog format to digital format, they will appear as chains of 0s and 1s, then the PC can handle them. So, we must be able to digitize our data. Pour text, sounds, and pictures into a funnel, from where they emerge as 0s and 1s: Let us see how this can be accomplished. q Next page q Previous page Learn more [top] Read more about the boot process and system bus in Module 2b Read more about I/O buses in module 2c Read more about the motherboard chip set in module 2d Read more about RAM in module 2e Read about EIDE in module 5b [Main page] [Contact] [Karbos Dictionary] [The Software Guides]http://www.karbosguide.com/hardware/module1a1.htm (4 of 5)7/27/2004 4:05:11 AM

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KarbosGuide.com. Module 1a. About data. KarbosGuide.com. Module 1a2. About Bytes Contents: q Next page q Previous page q Introduction q ASCII q About text and code q Data in files Introduction The most basic data processing is word processing. Let us use that as an example. When we do word processing, we work at a keyboard similar to a typewriter. There are 101 keys, where we find the entire alphabet A, B, C, etc. We also find the digits from 0 to 9 and all the other characters we need:,.-;():_?!"#*%&etc.. All these characters must be digitized. They must be expressed in 0s and 1s. Bits are organized in groups of 8. A group of 8 bits is called a byte. 8 bits = 1 byte, that is the system. Then, what can we do with bytes? First, let us see how many different bytes we can construct. A byte is an 8 digit number. We link 0s and 1s in a pattern. How many different ones can we make? Here is one: 01110101, and here is another: 10010101. We can calculate that you can make 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 different patterns, since each of the 8 bits can have 2 values. q 28 (two in the power of eight) is 256. Then there are 256 different bytes! Now we assign a byte to each letter and other characters. And since we have 256 patterns to choose from, there is plenty of room for all. Here you see some examples of thehttp://www.karbosguide.com/hardware/module1a2.htm (1 of 5)7/27/2004 4:05:22 AM

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KarbosGuide.com. Module 1a. About data. The ASCII table is divided in 3 sections: q Non printable system codes between 0 and 31. q "Lower ASCII" between 32 and 127. This part of the table originates from older, American systems, which worked on 7 bit character tables. Foreign letters, like Ø and Ü were not available then. q "Higher ASCII" between 128 and 255. This part is programmable, in that you can exchange characters, based on which language you want to write in. Foreign letters are placed in this part. Learn more about the ASCII table in Module 1b An example Let us imagine a stream of bits sent from the keyboard to the computer. When you type, streams of 8 bits are sent to the computer. Let us look at a series of bits: 001100010011001000110011 Bits are combined into bytes (each 8 bits). These 24 bits are interpreted as three bytes. Let us read them as bytes: 00110001, 00110010, and 00110011. When we convert these byte binary numbers to decimal numbers, you will see that they read as 49, 50, and 51 in decimal numbers. To interpret these numbers, we have to look at the ASCII table. You will find that you have typed the numbers 1, 2, and 3. About text and code [top] Now we have seen the PCs user data, which are always digitized. But there are many different kinds of data in the PC. You can differentiate between 2 fundamental types of data: q Program code, which is data, that allows the PC to function. q User data, like text, graphics, sound. The fact is, that the CPU must have instructions to function. You can read more about this in the review of the CPU in module 3a. An instruction is a string of data, of 0s and 1s. The CPU is designed to recognize these instructions, which arrive together with the user input data tohttp://www.karbosguide.com/hardware/module1a2.htm (3 of 5)7/27/2004 4:05:22 AM

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KarbosGuide.com. Module 1a. About data. be processed. The program code is thus a collection of instructions, which are executed one by one, when the program runs. Each time you click the mouse, or hit a key on the keyboard, instructions are sent from your software (program) to the CPU, telling it what to do next. User data are those data, which tells the software how to respond. The letters, illustrations, home pages, etc., which you and I produce, are created with appropriate software. Files [top] Both program code and user data are saved as files on the hard disk. Often, you can recognize the type of file by its suffix. Here are some examples: Content File name Program code START.EXE, WIN.COM, HELP.DLL, VMM32.VXD User data LETTER.DOC, HOUSE.BMP, INDEX.HTM This is written as an introduction to naming files. The file name suffix determines how the PC will handle the file. You can read about this subject in some of my books, e.g. "DOS - teach yourself" (only available in Europe. q Next page q Previous page Learn more [top] Read more about the boot process and system bus in Module 2b Read more about I/O buses in module 2c Read more about the motherboard chip set in module 2d Read more about RAM in module 2ehttp://www.karbosguide.com/hardware/module1a2.htm (4 of 5)7/27/2004 4:05:22 AM

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An illustrated Guide to MotherboardsKarbosGuide.com. Module 2a.1The PC and its motherboardThe contents: q Introduction to the PC q Next page q The PC construction q Previous q The motherboard (motherboard) page q POST and other ROM (BIOS etc.) Please click to support our work!Introduction to the PCThe technical term for a PC is micro data processor . That name is no longer in common use. However, it places the PCin the bottom of the computer hierarchy:q Supercomputers and Mainframes are the largest computers - million dollar machines, which can occupy more thanone room. An example is IBM model 390.q Minicomputers are large powerful machines. They typically serve a network of simple terminals. IBMs AS/400 is anexample of a minicomputer.q Workstations are powerful user machines. They have the power to handle complex engineering applications. Theyuse the UNIX or sometimes the NT operating system. Workstations can be equipped with powerful RISC processorslike Digital Alpha or MIPS.q The PCs are the Benjamins in this order: Small inexpensive, mass produced computers. They work on DOS,Windows , or similar operating systems. They are used for standard applications.The point of this history is, that Benjamin has grown. He has actually been promoted to captain! Todays PCs are justas powerful as minicomputers and mainframes were not too many years ago. A powerful PC can easily keep up withthe expensive workstations. How have we advanced this far?http://www.karbosguide.com/hardware/module2a1.htm (1 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to MotherboardsPlease click the banners to support our work! The PCs success [top]The PC came out in 1981. In less than 20 years, it has totally changed our means of communicating. When the PC wasintroduced by IBM, it was just one of many different micro data processors. However, the PC caught on. In 5-7 years,it conquered the market. From being an IBM compatible PC, it became the standard.If we look at early PCs, they are characterized by a number of features. Those were instrumental in creating the PCsuccess.q The PC was from the start standardized and had an open architecture.q It was well documented and had great possibilities for expansion.q It was inexpensive, simple and robust (definitely not advanced).The PC started as IBMs baby. It was their design, built over an Intel processor (8088) and fitted to Microsofts simpleoperating system MS-DOS.Since the design was well documented, other companies entered the market. They could produce functionable copies(clones) of the central system software (BIOS). The central ISA bus was not patented. Slowly, a myriad of companiesdeveloped, manufacturing IBM compatible PCs and components for them.The Clone was born. A clone is a copy of a machine. A machine, which can do precisely the same as the original (readBig Blue - IBM). Some of the components (for example the hard disk) may be identical to the original. However, theClone has another name (Compaq, Olivetti, etc.), or it has no name at all. This is the case with "the real clones."Today, we differentiate between:q Brand names, PCs from IBM, Compaq, AST, etc. Companies which are so big, so they develop their own hardwarecomponents.q Clones, which are built from standard components. Anyone can make a clone.Since the basic technology is shared by all PCs, I will start with a review of that. The PC construction [top]The PC consists of a central unit (referred to as the computer) and various peripherals. The computer is a box, whichcontains most of the working electronics. It is connected with cables to the peripherals.On these pages, I will show you the computer and its components. Here is a picture of the computer:http://www.karbosguide.com/hardware/module2a1.htm (2 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to MotherboardsHere is a list of the PC components. Read it and ask yourself what the words mean. Do you recognize all thesecomponents? They will be covered in the following pages. Components in the central unit - the computer Peripherals The motherboard: CPU, RAM, cache, Keyboard and ROM chips with BIOS and start-up programs. mouse. Chip sets (controllers). Ports, buses and expansion Joystick slots. Monitor Printer Drives: Hard disk(s), floppy drive(s), CD-ROM, etc. Scanner Loudspeakers External drives Expansion cards: Graphics card (video adapter), External tape station network controller, SCSI controller. External modem Sound card, video and TV card. Internal modem and ISDN card.So, how are the components connected. What are their functions, and how are they tied together to form a PC? Thatis the subject of Click and Learn. So, please continue reading...http://www.karbosguide.com/hardware/module2a1.htm (3 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to Motherboards The von Neumann Model of the PC [top]Computers have their roots 300 years back in history. Mathematicians and philosophers like Pascal, Leibnitz, Babbageand Boole made the foundation with their theoretical works. Only in the second half of this century was electronicscience sufficiently developed to make practical use of their theories.The modern PC has roots that go back to the USA in the 1940s. Among the many scientists, I like to remember Johnvon Neumann (1903-57). He was a mathematician, born in Hungary. We can still use his computer design today. Hebroke computer hardware down in five primary parts:q CPUq Inputq Outputq Working memoryq Permanent memoryActually, von Neumann was the first to design a computer with a working memory (what we today call RAM). If weapply his model to current PCs, it will look like this:http://www.karbosguide.com/hardware/module2a1.htm (4 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to MotherboardsAll these subjects will be covered. Data exchange - the motherboard [top]The ROM chips contain instructions, which are specific for that particular motherboard. Those programs andinstructions will remain in the PC throughout its life; usually they are not altered.Primarily the ROM code holds start-up instructions. In fact there are several different programs inside the start-upinstructions, but for most users, they are all woven together. You can differentiate between:q POST (Power On Self Test)q The Setup instructions, which connect with the CMOS instructionsq BIOS instructions, which connect with the various hardware peripheralsq The Boot instructions, which call the operating system (DOS, OS/2, or Windows )All these instructions are in ROM chips, and they are activated one by one during start-up. Let us look at each part. The suppliers of system software [top]All PCs have instructions in ROM chips on the motherboard. The ROM chips are supplied by specialty softwaremanufacturers, who make BIOS chips. The primary suppliers are:q Phoenixq AMI ( American Megatrends )q AwardYou can read the name of your BIOS chip during start-up. You can also see the chip on the system board. Here is apicture (slightly blurred) of an Award ROM chip:http://www.karbosguide.com/hardware/module2a1.htm (5 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to MotherboardsHere is an AMI chip with BIOS and start-up instructions:Let us look at the different components inside the ROM chip.q Next pageq Previous page Learn more [top]Read more about the boot process and system bus in Module 2bRead more about I/O buses in module 2cRead more about the motherboard chip set in module 2dRead more about RAM in module 2eRead about EIDE in module 5bI also recommend two books for further studies. Gunnar Forst: "PC Principles", from MIT is excellent. Also "The WinnL. Rosch Hardware Bible" from Brady covers the same subjects. Also "PC Intern" from Abacus is fine.Links to BIOS information:Mr BIOS FAQhttp://www.karbosguide.com/hardware/module2a1.htm (6 of 7)7/27/2004 4:05:28 AM

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An illustrated Guide to Motherboards Please click the banners to support our work! Click & Learn. Module 2a.2 The system software on the motherboard The contents: q The Setup program q Next page q The POST q Previous page q The CMOS RAM q Opening the Setup program Articles written by Michael B. Karbo The Setup programs [top] There are three elements in the start-up part of the ROM chip: q The Initializing routine, which sets up the BIOS functions. The adapter ROM is integrated. A table covering all the BIOS programs is constructed. This is often called the interrupt vectors. q The POST (the test programs) q The disk bootstrap loader, which calls upon the operating system.http://www.karbosguide.com/hardware/module2a2.htm (1 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards These programs are stored in the ROM chip, and they are activated one by one during the PC start- up. The POST Power On Self Test is the first instruction executed during start-up. It checks the PC components and that everything works. You can recognize it during the RAM test, which occurs as soon as you turn power on. You may follow the checks being executed in this order, as the information are gathered: 1) Information about the graphics adapter 2) Information about the BIOS (name, version) 3) Information about the RAM (being counted) As users, we have only limited ability to manipulate the POST instructions. But certain system boards enable the user to order a quick system check. Some enable the user to disable the RAM test, thereby shortening the duration of the POST. The duration of the POST can vary considerably in different PCs. On the IBM PC 300 computer, it is very slow. But you can disrupt it by pressing [Esc]. Error messages If POST detects errors in the system, it will write error messages on the screen. If the monitor is not ready, or if the error is in the video card, it will also sound a pattern of beeps (for example 3 short and one long) to identify the error to the user. If you want to know more of the beeps, you can find explanations on the Award, AMI and Phoenix web sites. For instance you will receive error messages if the keyboard is not connected or if something is wrong with the cabling to the floppy drive. POST also reads those user data, which are found in the CMOS. This is discussed in the following chapter. The bootstrap loader The last part of the BIOS execution at start-up is the bootstrap loader. It is a tiny program, which only has one task: to find the bootsector on a disk (hard disk, floppy or another boot-drive). The DOS Boot Record (DBR) also holds a media descriptor as well as information on the OS version. Please read module 6a4 on this issue. You can use DiskEdit (included in the "Norton Utilities") to read view the contents of the boot sector.http://www.karbosguide.com/hardware/module2a2.htm (2 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards When the disk holds no boot strap routine, you get an error message like "Non-system disk, replace with system disk and press any key". The bootstrap loader is the last step in BIOS execution during start-up. It hands over the control to the bootstrap routine found on the boot disk. The OS is being loaded. CMOS RAM [top] CMOS stands for Complementary Metal Oxide Semiconductor. In PC’s there is a small amount of memory in a special CMOS RAM chip. The data is maintained with electric power from a small battery. CMOS is only a medium for storage. It could be used for any type of data. Here, it holds important system data, values to be used during the start process. These information take up maybe 100 orhttp://www.karbosguide.com/hardware/module2a2.htm (3 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards 200 bytes of data, and storage in the CMOS makes them instantly available to the POST and BIOS programs (loaded from ROM) during the start-up. The values are regarding: q Floppy and hard disk drives q The keyboard q The CPU, cache, chip set values, RAM type q Date and time q Much more ... These data have to be set up correctly, and they are read during the start-up to make the PC operable. Two types of data CMOS data can be divided in two groups: q Data, which POST cannot find during the system test. q Data, which contain user options. For example, POST cannot by itself find sufficient information about the floppy drive(s). Floppy drives are so "dumb," that POST cannot read whether they are floppy drives or not, nor what type. About the same goes for IDE hard disks, while EIDE hard disks are a little more "intelligent," However, POST still needs assistance to identify them 100% correctly. The same goes for RAM: POST can count how much RAM is in the PC. However, POST cannot always detect whether it is FPM, EDO or SD RAM. Since the CPU and BIOS reads data from RAM chips differently, depending on the RAM type, the type must be identified to setup the correct timing.http://www.karbosguide.com/hardware/module2a2.htm (4 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards The configuration of CMOS data The PC must be configured, be supplied with this information. That is done in the factory or store, where it is assembled. This information is stored in CMOS, where they stay. CMOS data only need to be updated, when different or additional hardware components are installed. This could be a different type hard disk or floppy disks or an new RAM type. Often the user can do this him/herself. Other data in CMOS contain various user options . This is data, which you can write to CMOS. For example, you can adjust date and time, which the PC then adjusts every second. You can also choose between different system parameters. Maybe you want a short system check instead of a long one. Or if you want the PC to try to boot from hard disk C before trying floppy disk A, or vice versa. These options can be written to CMOS. Many of the options are of no interest to the ordinary user. These are options, which regard controller chips on the motherboard, which can be configured in different ways. Ordinarily, there is no need to make such changes. The motherboard manufacturer has already selected the optimal configurations. They recommend in their manuals, that you do not change these default settings. We can conclude, that CMOS data are essential system data, which are vital for operation of the PC. Their special feature is, that they are user adjustable. Adjustments to CMOS are made during start-up. Opening the Setup program [top] You communicate with the BIOS programs and the CMOS memory through the so-called Setup program. This gives us a very simple user interface to configuring the PC with these vital data. Typically you reach the Setup program by pressing [Delete] immediately after you power up the PC. That brings you to a choice of setup menus. You leave Setup by pressing [Esc], and choose "Y" to restart the PC with the new settings. Generally, you should not change these settings, unlesshttp://www.karbosguide.com/hardware/module2a2.htm (5 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards you know precisely what you are doing. Here you see the start menu of the American Megatrends BIOS Setup program, which has a kind of graphical user interface. You are supposed to use the mouse: q Next page q Previous page Learn more [top] Read more about the boot process and system bus in Module 2b Read more about I/O buses in module 2c Read more about the motherboard chip set in module 2d Read more about RAM in module 2e Read about EIDE in module 5bhttp://www.karbosguide.com/hardware/module2a2.htm (6 of 7)7/27/2004 4:05:35 AM

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An illustrated Guide to Motherboards Please click the banners to support our work! KarbosGuide.com. Module 2a.3 Using the system software of the motherboard The contents: q What use of Setup program? q Next page q Modifying the boot sequence q Previous page q Images from the setup programhttp://www.karbosguide.com/hardware/module2a3.htm (1 of 6)7/27/2004 4:05:47 AM

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An illustrated Guide to Motherboards What can I use the Setup program for? [top] The Setup program can do many things for you. However, be careful. You should not change any values within the menus, unless you know what you are doing. Otherwise your PC may not function properly. You have to enter Setup, if you install a different type or additional disk drive in your PC. Certain BIOSs will also need adjustment of its settings, if a CDROM drive is installed on one of the EIDE channels. The Standard values The standard values in the CMOS Setup are used to configure: q The date and time. q The keyboard. q The display. q The diskette drive. q EIDE units number 1-4 (typically hard disks and CD-ROM-drive). The values for date and time are stored in the CMOS RAM. You can always change them, from Setup or from DOS, Windows or any other OS. The keyboard - obviously it has to be there. But it is possible to configure the PC to work without a keyboard. Otherwise the PC will error if the keyboard is missing. The display is always VGA. From older times the Setup gives you options as EGA, CGA and MDA. You wont need them! Diskette drive has to be selected. You can choose to have A: or B: or both. Each drive can be of fivehttp://www.karbosguide.com/hardware/module2a3.htm (2 of 6)7/27/2004 4:05:47 AM

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An illustrated Guide to Motherboards types or more. You probably have the 1.44 MB floppy drive. You choose among the options using [PgUp] and [PgDn]. Modern super floppies like Zip and LS120 are not to be installed as diskette drives, they are EIDE units. The hard disk is the most important unit to install in this part of the Setup. With the modern motherboards and the EIDE drives you may experience an automatic configuration during the Auto detect . In other situations you have to run the auto detect yourself. With older drives, you have to enter all the CHS-values for the drive (number of cylinders, heads and sectors. The BIOS Feature Setup The Feature Setup is the next layer in the CMOS setup. Here you can choose among options like: q Quick execution of POST (a good thing). q Choice of boot device EIDE/SCSI. If you have both types of hard drives, which one is to be booted? q The boot sequence. q .... Modifying the boot sequence You can change the boot sequence from A:, C: to C:, A:. That means, that the PC will not try to boot from any diskette in the A drive. This will protect you from certain virus attacks from the boot sector. Also, the boot process will not be blocked by any diskette in the A drive. If you need to boot from A- drive (for example, if you want to install Windows 98), you have to enter Setup again, and change the boot sequence to A:, C:. That is no problem. Power Management You also use the Setup program to regulate the power management , which is the power saving features in the motherboard. For example, you can make the CPU shut down after one minute of no activity. There are plenty of settings available in this area. The power management functions found on the PC’s motherboard will cooperate with the operating system. Especially Windows 98 is very good at using the power management. Password Protection You can protect the Setup program with a password. This is used widely in schools, where the teachers do not want the little nerds to make changes in the setup. Please remember the password (write it down in the motherboard manual). If you forget it you have to remove the battery from the motherboard. Then all user input to the CMOS is erased - including the password. [top] Images from the Setup programhttp://www.karbosguide.com/hardware/module2a3.htm (3 of 6)7/27/2004 4:05:47 AM

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An illustrated Guide to Motherboards Here is a scanned image from a Setup program. It belongs a very fine board from ASUS. Here you see the "BIOS Feature Setup," where you can select start-up choices: Here we are in the special "Chip set Feature Setup." These choices relate to the chip sets and, most likely, need no changes:http://www.karbosguide.com/hardware/module2a3.htm (4 of 6)7/27/2004 4:05:47 AM

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An illustrated Guide to Motherboards q Next page q Previous page Learn more [top] Module 2b. About the boot process and system bus Read more about I/O buses in module 2c Read more about the motherboard chip set in module 2d Read more about RAM in module 2e Read about EIDE in module 5b I also recommend two books for further studies. Gunnar Forst: "PC Principals", from MIT is excellent. Also "The Winn L. Rosch Hardware Bible" from Brady covers the same subjects. Also "PC Intern" from Abacus is fine. Links to BIOS information:http://www.karbosguide.com/hardware/module2a3.htm (5 of 6)7/27/2004 4:05:47 AM

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An illustrated Guide to MotherboardsKarbosGuide.com. Module 2a.4.The system software of hardwareThe contents: q Next page q Previous pageThe BIOS in adapter ROM [top]During the start-up process the BIOS programs are read from the ROM circuits. BIOS stands for Basic InputOutput System and it is small program routines which controls specific hardware units.For instance you have a BIOS routine which reads the keyboard:http://www.karbosguide.com/hardware/module2a4.htm (1 of 4)7/27/2004 4:05:55 AM

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An illustrated Guide to MotherboardsThe BIOS is a part of the modular design of the IBM Compatible PC. The OS and other programs access thehardware units by making requests to the BIOS routines.BIOS typically occupies 64 KB, and the programs are stored in ROM chips on the motherboard.The reserved areasIn the original PC design we only had 1 MB of RAM. This memory was adressed using hex numbers, so each bytehad its own address going from 00000h to FFFFFh.Important parts of the system software is mapped into this range, where we also find two reserved areas: Hex address Kilobytes Occupied by C0000- 768-800 BIOS from the video card C8000 F0000 - 960- BIOS from the FFFFF 1024 MotherboardThese two ranges are reserved for this special adapter ROM. Other adapters cannot map their BIOS routines intothese addresses.If it is setup to shadowing ("Shadow RAM" in the Setup utility), then this BIOS code is copied into RAM. If not, ithas to be read directly from the ROM circuit. The last access is slower.BIOS on many adaptershttp://www.karbosguide.com/hardware/module2a4.htm (2 of 4)7/27/2004 4:05:55 AM

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An illustrated Guide to MotherboardsThere are BIOS codes on many adapters (expansion cards). The adapters are external hardware, which areconnected to and “integrated” with the motherboard during the hardware configuration and internalizing.The adapters hold their own BIOS code making them functional. This BIOS must be included during theconfiguration. Therefore, the adapter ROM is read during start-up, and the program code is “woven” togetherwith other BIOS programs and the CMOS data. It is all written into RAM, where it is ready for the operatingsystem, as you can see here:The BIOS routines are not always in use. They can be regarded as basic program layers in the PC, giving it asimple functionality.Many programs routinely bypass BIOS. In that case, they "write direct to hardware", as we say. Windowscontains program files, which can be written directly to all kinds of hardware - bypassing BIOS routines. Oneexample is the COM ports. If you use the BIOS routines connected with them, you can transmit only at max.9600 baud on the modem. That is insufficient. Therefore, Windows will assume control over the COM port.BIOS updateBIOS programs can be updated . The modern motherboard has the BIOS instructions in flash ROM, which can beupdated. You can get new BIOS software from your supplier or on the Internet, which can be read onto themotherboard. The loading is a special process, where you might need to change a jumper switch on themotherboard. Usually, you do not need to do this, but it is a nice available option. ATX motherboards [top]The latest PC electronic standard is called ATX. It consists of a new type motherboard with a specific physicaldesign like the traditional board (30.5 cm X 19 cm). However the board has been shifted 90 degrees for a betterhttp://www.karbosguide.com/hardware/module2a4.htm (3 of 4)7/27/2004 4:05:55 AM

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An illustrated Guide to Motherboardsplacing of the units.The I/O connectors COM1, COM2 and LPT, keyboard, mouse and USB are mounted directly on the motherboard.The ATX board requires specifically designed chassises with an I/O access opening measuring 1¾ by 6¼ inch.ATX is designed by Intel, but has gained general acceptance.The ATX motherboard is more ”intelligent” than the ordinary type. In a few years, it will be wide spread. Itincludes advanced control facilities, where the BIOS program continually checks the CPU temperature andvoltages, the cooling fans RPM, etc. If over heating occurs, the PC will shut down automatically. The PC can alsobe turned on by for example modem signals, since the power supply is controlled by the motherboard. The on/offbutton will turn the PC "down" without turning it completely off.If you want a PC designed for the future, the ATX layout is what you should go for.q Next pageq Previous page Learn more [top]Module 2b. About the boot process and system busRead more about I/O buses in module 2cRead more about the motherboard chip set in module 2dRead more about RAM in module 2eRead about EIDE in module 5bI also recommend two books for further studies. Gunnar Forst: "PC Principals", from MIT is excellent. Also "TheWinn L. Rosch Hardware Bible" from Brady covers the same subjects. Also "PC Intern" from Abacus is fine.Links to BIOS information:BIOS GuideMr BIOS FAQ [Main page] [Contact] [Karbos Dictionary] [The Windows 98 pages]Copyright (c) 1996-2001 by Michael B. Karbo. www.karbosguide.com.http://www.karbosguide.com/hardware/module2a4.htm (4 of 4)7/27/2004 4:05:55 AM

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An illustrated Guide to the PC System BUS KarbosGuide.com. Module 2b1. About the System Bus In this module, you can read about the following subjects, which add to our tour of the PC: q The boot process q Next page q Data on the motherboard q Previous page The boot process [top] The last step in the PC start-up is reading the operating system. The start-up program is instructed to find the Master Boot Record. This is located in the very first sector on either hard disk (C) or floppy drive A. From the MBR it reads the boot-strap which points to the location of the startup files of the Operating System. By default, the PC will look for a boot sector in floppy drive A. That is why the PC "drops dead" if there is a different diskette in A drive. If there is no diskette in A drive, the start-up program will search for the boot sector on hard drive C. When the boot sector is found, a small program segment (boot-strap) is read from there. The boot-strap then takes over control of the PC. The start-up program has done its job. Now DOS, Windows , or another operating system takes control. Read more about boot sectors, etc. in module 6a, which deals with file systems. Here is an illustration of the start-up process:http://www.karbosguide.com/hardware/module2b1.htm (1 of 4)7/27/2004 4:05:57 AM

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An illustrated Guide to the PC System BUS The data flow on the motherboard [top] On the motherboard, you will find the CPU, which is the "brain" of the PC and the buses. The buses are the nerve system of the motherboard. They connect the CPU to all the other components. There are at least three buses, which you can see below. You can read more about those on the following pages. The buses are the PCs expressways. They are "wires" on the circuit board, which transmit data between different components. One "wire" can move one bit at a time. In the following text, we start from a typical Pentium board. We will look at buses, chip sets and CPUs. Here is an illustration of some of the motherboard "logic." You can print it:http://www.karbosguide.com/hardware/module2b1.htm (2 of 4)7/27/2004 4:05:57 AM

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An illustrated Guide to the PC System BUS q Next page q Previous page Learn more [top] Read more about the motherboards chip set in module 2d Read more about RAM in module 2e [Main page] [Contact] [Karbos Dictionary] [The Software Guides]http://www.karbosguide.com/hardware/module2b1.htm (3 of 4)7/27/2004 4:05:57 AM

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An illustrated Guide to the PC System BUS KarbosGuide.com. Module 2b2. About the System Bus In this module, you can read about the following subjects, which add to our tour of the PC: q PC buses, an intro q Next page q The system bus q Previous page q 66 MHz bus q 100 MHz bus Introduction to the PC buses [top] The PC receives and sends its data from and to buses. They can be divided into: q The system bus, which connects the CPU with RAM q I/O buses, which connect the CPU with other components.http://www.karbosguide.com/hardware/module2b2.htm (1 of 6)7/27/2004 4:05:59 AM

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An illustrated Guide to the PC System BUS The point is, that the system bus is the central bus. Actually, it connects to the I/O buses, as you can see in this illustration. It is not completely correct, since the architecture is much more complex, but it shows the important point, that the I/O-buses usually derive from the system bus: You see the central system bus, which connects the CPU with RAM. A bridge connects the I/O buses with the system bus and on to RAM. The bridge is part of the PC chip set, which will be covered in module 2c. 3 different I/O buses [top] The I/O buses move data. They connect all I/O devices with the CPU and RAM. I/O devices are those components, which can receive or send data (disk drives, monitor, keyboard, etc. ). In a modern Pentium driven PC, there are two or three different I/O buses: q The ISA bus, which is oldest, simplest, and slowest bus. q The PCI bus, which is the fastest and most powerful bus. q The USB bus, which is the newest bus. It may in the long run replace the ISA bus. The three I/O buses will be described later. Here, we will take a closer look at the PCshttp://www.karbosguide.com/hardware/module2b2.htm (2 of 6)7/27/2004 4:05:59 AM

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An illustrated Guide to the PC System BUS fundamental bus, from which the others are branches from. The system bus [top] The system bus connects the CPU with RAM and maybe a buffer memory (L2-cache). The system bus is the central bus. Other buses branch off from it. The system bus is on the motherboard. It is designed to match a specific type of CPU. Processor technology determines dimensioning of the system bus. At the same time, it has taken much technological development to speed up "traffic" on the motherboard. The faster the system bus gets, the faster the remainder of the electronic components must be.. The following three tables show different CPUs and their system buses: Older CPUs System bus width System bus speed 8088 8 bit 4.77 MHz 8086 16 bit 8 MHz 80286-12 16 bit 12 MHz 80386SX-16 16 bit 16 MHz 80386DX-25 32 bit 25 MHz We see, that system bus speed follows the CPUs speed limitation. First at the fourth generation CPU 80486DX2-50 are doubled clock speeds utilized. That gives the CPU a higher internal clock frequency. The external clock frequency, used in the system bus, is only half of the internal frequency: CPUs in the 80486 family System bus width System bus speed 80486SX-25 32 bit 25 MHz 80486DX-33 32 bit 33 MHz 80486DX2-50 32 bit 25 MHz 80486DX-50 32 bit 50 MHzhttp://www.karbosguide.com/hardware/module2b2.htm (3 of 6)7/27/2004 4:05:59 AM

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An illustrated Guide to the PC System BUS boards. In the Pentium-II modules 70-80% of the traffic is inside the SEC module, holding both L1 and L2 cache. And the module has its own speed independent of the system bus. With the K6 the increase of system bus speed gives a vastly improved performance since the traffic between L1 and L2 cache crosses the system bus. 133 MHz Intels 820 and 815 chipsets to be used with Pentium III work with 133 MHz RAM as well as several VIA chipsets do. In AMDs Athlon the system bus architecture was changed; it is not really a system bus any longer. Hence Athlon chipsets may work with many types of RAM. Processor Chip set System bus speed CPU speed Intel Pentium II 82440BX 100 MHz 350, 400, 450 MHz 82440GX AMD K6-2 Via MVP3ALi Aladdin V 100 MHz 250, 300, 400 MHz Intel Pentium II Xeon 82450NX 100 MHz 450, 500 MHz Intel Pentium III i815 133 MHz 600, 667 MHz and up i820 AMD Athlon VIA KT133 and others 200 MHz 600 - 1000 MHz With the 100 MHz bus, we dicovered that motherboards have to be well constructed with good power supply and many capacitors. Newer buses As mentioned under AMD Athlon, "system bus" is not that relevant a term looking at modern motherboards. The bus to RAM becomes separated from the other buses and this design opens up for better bandwidth between the CPU and the RAM. Intels use of Rambus RAM working at 400 MHz as well as PC2100 RAM on non-Intel boards follows this trend. The DDRAM operates with interfaces working at 200, 266 and 333 MHz. q Next page q Previous pagehttp://www.karbosguide.com/hardware/module2b2.htm (5 of 6)7/27/2004 4:05:59 AM

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An illustrated Guide to the PC System BUS Learn more [top] Read more about the motherboards chip set in module 2d Read more about RAM in module 2e [Main page] [Contact] [Karbos Dictionary] [The Software Guides] Copyright (c) 1996-2001 by Michael B. Karbo. www.karbosguide.com.http://www.karbosguide.com/hardware/module2b2.htm (6 of 6)7/27/2004 4:05:59 AM

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An illustrated Guide to I/O-buses KarbosGuide.com. Module 2c.1 About the I/O buses On these pages, you can read about the important system bus derivatives, the different I/O buses: q Introduction to the I/O buses q Next page q Technical and historical background for the I/O buses q Previous pagehttp://www.karbosguide.com/hardware/module2c1.htm (1 of 7)7/27/2004 4:06:02 AM

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An illustrated Guide to I/O-buses Introduction to the I/O buses [top] We have seen before, that the PCs buses are the fundamental data "highways" on the system board. The "first" bus is the system bus, which connects the CPU with RAM. In older designs it was a local bus. In newer designs this bus is called the front side bus (FSB). The typical local bus has a speed and width depending on the type CPU installed on the motherboard. Typically, the system bus will be 64 bits wide and run at 66, 100 or 133 MHz. These high speeds create electrical noises and other problems. Therefore, the speed must be reduced for data reaching the expansion cards and other more peripheral components. Very few expansion cards can operate at more than 40 MHz. Then the electronics shut down. The chips can just not react faster. Therefore, the PC has additional buses. Originally only one bus However, the first PCs had only one bus, which was common for the CPU, RAM and I/O components: The older first and second generation CPUs ran at relatively low clock frequencies, and all system components could keep up with those speeds. RAM on adapters Among other things, that allowed additional RAM to be installed in expansion slots in the PC,http://www.karbosguide.com/hardware/module2c1.htm (2 of 7)7/27/2004 4:06:02 AM

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An illustrated Guide to I/O-buses by installing an adapter in a vacant expansion slot. An adapter, where RAM was mounted: This setup would be unthinkable today. However it is truely a local bus. All units are united on one bus using the same clock. First in 1987, Compaq figured out how to separate system bus from I/O bus, so they could run at different speeds. This multi-bus architecture has been industry standard ever since. Modern PCs also have more than one I/O bus. What does an I/O bus do? [top] I/O buses connect the CPU to all other components, except RAM. Data are moved on the buses from one component to another, and data from other components to the CPU and RAM. The I/O buses differ from the system bus in speed. Their speed will always be lower than the system bus speed. Over the years, different I/O buses have been developed. On modern PCs, you will usually find four buses:http://www.karbosguide.com/hardware/module2c1.htm (3 of 7)7/27/2004 4:06:02 AM

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An illustrated Guide to I/O-buses q The ISA bus, which is an old low speed bus, soon to be excluded from the PC design. q The PCI bus, which is a new high speed bus. q The USB bus (Universal Serial Bus), which is a new low speed bus. q The AGP bus which solely is used for the graphics card. As mentioned earlier, I/O buses are really extensions to the system bus. On the motherboard, the system bus ends in a controller chip, which forms a bridge to the I/O buses. All in all, the buses have had a very central placement in the PCs data exchange. Actually, all components except the CPU communicate with each other and with RAM via the different I/O buses. Here you see a demonstration of this logic:http://www.karbosguide.com/hardware/module2c1.htm (4 of 7)7/27/2004 4:06:02 AM

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An illustrated Guide to I/O-buses The physical aspects of the I/O buses [top] Physically, the I/O bus consists of tracks on the printed circuit board. These tracks are used as: q Data tracks, which each can move one bit at a time q Address tracks, which identify where data should be sent to q Other tracks for clock ticks, voltage, verification signals, etc. When data are sent on the bus, they must be supplied with a receiver. Therefore, each device on the bus has an address. Similarly, the RAM is divided in sections, each having its address. Prior to sending data, a number is sent on the address track, to identify where the data should be sent to. The bus width The number of data tracks determine the data transfer capacity. The ISA bus is slow, partly because it only has 16 data tracks. The modern PCs send 32 bits per clock tick. On the ISA bus, 32 bits must be divided in two packages of 16 bits. This delays the data transfer. Another I/O bus concept is wait states. Wait states Wait states are small pauses. If an ISA adapter cannot keep up with the incoming data flow, its controller sends wait states to the CPU. Those are signals to the CPU to "hold on for a sec." A wait state is a wasted clock tick. The CPU skips a clock tick, when not occupied. Thus the old and slow ISA adapter can significantly reduce the operating speed of a modern computer. Another aspect is the IRQ signals, which the components use to attract attention from the CPU. That and the concepts DMA and bus mastering, are described in module 5, which deals with adapters. Technical and historical background for the I/ O buses [top] In modern PCs you only find the PCI and ISA buses (besides USB, which we do not knowhttp://www.karbosguide.com/hardware/module2c1.htm (5 of 7)7/27/2004 4:06:02 AM

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An illustrated Guide to I/O-busesKarbosGuide.com. Module 2c.2About the ISA bus and other old PC busesThe contents: q Introduction to the ISA bus q Next page q MCA, Eisa and VLB buses q Previous page Introduction to the ISA busSince about 1984, standard bus for PC I/O functions has been named ISA (Industry Standard Architecture). It isstill used in all PCs to maintain backwards compatibility. In that way modern PCs can accept expansion cards of theold ISA type.ISA was an improvement over the original IBM XT bus, which was only 8 bit wide. IBMs trademark is AT bus.Usually, it is just referred to as ISA bus.ISA is 16 bit wide and runs at a maximum of 8 MHz. However, it requires 2-3 clock ticks to move 16 bits of data.The ISA bus works synchronous with the CPU. If the system bus is faster than 10 MHz, many expansion boardsbecome flaky and the ISA clock frequency is reduced to a fraction of the system bus clock frequency.The ISA bus has an theoretical transmission capacity of about 8 MBps. However, the actual speed does not exceed1-2 MBps, and it soon became too slow.Two faceshttp://www.karbosguide.com/hardware/module2c2.htm (1 of 5)7/27/2004 4:06:04 AM

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An illustrated Guide to I/O-busesThe ISA bus has two "faces" in the modern PC:q The internal ISA bus, which is used on the simple ports, like keyboard, diskette drive, serial and parallel ports.q As external expansion bus, which can be connected with 16 bit ISA adapters.ISA slots are today mostly used for the common 16 bit SoundBlaster compatible sound cards.ProblemsThe problem with the ISA bus is twofold:q It is narrow and slow.q It has no intelligence.The ISA bus cannot transfer enough bits at a time. It has a very limited bandwidth. Let us compare the bandwidthsof ISA bus and the newer PCI bus: Bus Transmission time Data volume per transmission ISA 375 ns 16 bit PCI 30 ns 32 bitClearly, there is a vast difference between the capacity of the two buses. The ISA bus uses a lot of time for everydata transfer, and it only moves 16 bits in one operation.The other problem with the ISA bus is the lack of intelligence. This means that the CPU has to control the datatransfer across the bus. The CPU cannot start a new assignment, until the transfer is completed. You can observethat, when your PC communicates with the floppy drive, while the rest of the PC is waiting. Quite often the wholePC seems to be sleeping. That is the result of a slow and unintelligent ISA bus.Problems with IRQshttp://www.karbosguide.com/hardware/module2c2.htm (2 of 5)7/27/2004 4:06:04 AM

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An illustrated Guide to I/O-busesThe ISA bus can be a tease, when you install new expansion cards (for example a sound card). Many of theseproblems derive from the tuning of IRQ and DMA, which must be done manually on the old ISA bus.Every component occupies a specific IRQ and possibly a DMA channel. That can create conflict with existingcomponents. Read module 5 about expansion cards and these problems. The ISA bus is outAs described, the ISA bus is quite outdated and should not be used in modern pcs. There is a good chance, thatthis "outdated legacy technology" (quoting Intel) will disappear completely.The USB bus is the technology that will replace it. It has taken many years to get this working and accepted, but itworks now.Intels chip set 810 was the first not to include ISA support. MCA, EISA and VLB [top] In the 80s, a demand developed for buses more powerful than the ISA. IBM developed the MCA bus and Compaq and others responded with the EISA bus. None of those were Please support our particularly fast, and they never became particularly successful outside the server market. sponsor.MCAIBMs top of the line bus from 1987 is named Micro Channel Architecture. The MCA bus was a masterpiece, unifyingthe best bus technology from the mainframe design with the demands from the PC. However, contrary to the ISAbus, MCA is patented, and IBM demanded high royalty fees, when other PC manufacturers wanted to use it. Thusthe bus never became a great success, despite its advanced design. It ended up being a classic example of poormarketing strategy.The MCA bus is 32 bit wide and "intelligent." The cards configure themselves with respect to IRQ. Thus, they canbe installed without adjustments of jumper switches or other features. It works constantly at 10.33 MHz,asynchronous with the system bus.The MCA bus is also relatively fast with transfer rates of up to 40 MBps in 32 bit mode at 10.33 MHz. MCA requiresspecial adapters. There have never been too many adapters developed, since this bus is by and large used only inIBMs own PCs.EISAEISA is a bus from 1988-89. It is designed by the "Gang of Nine:" the companies AST, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse and Zenith. It came in response to IBMs patented MCA bus.EISA is built on the ISA bus; the connector has the same dimensions and old ISA cards fit into the slots. To keepthis compatibility, the EISA bus works at maximum 8 MHz. Like ISA, the bus bus is synchronous with the CPU at aclock frequency reduced to a fraction of the system bus clock frequency.http://www.karbosguide.com/hardware/module2c2.htm (3 of 5)7/27/2004 4:06:04 AM

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An illustrated Guide to I/O-busesEISA is compatible with ISA in the sense that ISA adapters can be installed in EISA slots. The EISA adapters hold asecond level of connectors in the button of the slot.However, EISA is much more intelligent than ISA. It has bus mastering, divided interrupts and self configuration. Itis 32 bit wide, and with its compressed transfers and BURST modegives a highly improved performance.But, like the MCA, it did not have great success. The EISA bus is still used in some servers.Vesa Local BusThis Bus called VLB for short. It is an inexpensive and simple technology. This bus only achieved status as aninterim phenomenon (in 1993-94). VLB was widely used on 486 motherboards, where the system bus runs at 33MHz. VLB runs directly with the system bus. Therefore, data transfer is at CPU speed, synchronous and in width.The problem with VLB was compatibility. Adapters and system system boards would not always work together.Vesa is an organization with about 120 members, mostly monitor and graphics card manufacturers. Therefore,most VLB cards were video cards.q Next pageq Previous page Learn more [top]Read module 5c about the modern I/O bus called USB.Read module 5a about expansion cards, where we evaluate the I/O buses from the port side.Read module 5b about AGP and module 5c about FirewireRead more about chip sets on the motherboard in module 2d.Read more about RAM in module 2e.Read Module 4b about hard disks.Read Module 4c about optical media (CDROM and DVD).Read Module 4d about super diskette and MO drives.Read module 7a about monitors, and 7b on graphics card.Read module 7c about sound cards, and 7d on digital sound and music. [Main page] [Contact] [Karbos Dictionary] [The Software Guides]http://www.karbosguide.com/hardware/module2c2.htm (4 of 5)7/27/2004 4:06:04 AM

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An illustrated Guide to I/O-buses KarbosGuide.com. Module 2c.3 About the PCI bus The contents: q Introducing the PCI bus q Next page q The internal and external face. q Previous page q The future design q NGIO Introducing the PCI bus [top] The PCI is the high speed bus of the 1990s. PCI stands for Peripheral Component Interconnect. This bus is made by Intel. It is used today in Please support our all PCs and other computers for connecting adapters, such as network- sponsor. controllers, graphics cards, sound cards etc. Some graphics cards however use the AGP-bus, which is a separate bus only intended for graphics.http://www.karbosguide.com/hardware/module2c3.htm (1 of 4)7/27/2004 4:06:06 AM